Error 400 when LLM response contains both Text and FunctionCall

Gemini API
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I’m using the gemini-2.0-flash-001 model with the Go API.

I have a model set up with a handful of function declarations. I noticed that whenever a call to genai.ChatSession.SendMessage(ctx, inputParts...) returns a top candidate that contains both an (empty) Text part and a FunctionCall part, then the next call to genai.ChatSession.SendMessage(ctx, inputParts...) – where inputParts is a FunctionResponse – would invariably fail with an error 400 and an empty error message: googleapi: Error 400:.

Changing the prompt slightly would avoid the mixed Text and FunctionCall outputs, and the subsequent 400 error for the next call.

Expected behavior: Tolerate LLM responses with mixed Text and FunctionCall parts to allow the subsequent call with a FunctionResponse to pass.

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